Cave Beetles Research Articles

A Study about Human Interference on the Two Caves of Udayagiri of Odisha State, India in the Viral Pandemic Year (2020), in Comparison with a Normal Year (2021)

The subterranean karst system with its unexplored fauna and flora is an area of curiosity for researchers. The present study on the faunal diversity of the twin caves of Udayagiri, located in the capital of Odisha, is one of such less explored terrains. The seasonal variation of the vertebrates (including bats, geckos, frogs) and invertebrates (including ants and cave beetles) is compared with temporal changes in the two caves of Udayagiri, Bhubaneswar, Odisha, India in the COVID 19 pandemic year of 2020 with the normal year of 2021. These caves are a tourist destination; the faunal distribution is disturbed by human activities. The comparative diversity of animals in such caves is of high implication to understand the bio-geological phenomena and its reflex to anthropogenic activities.

Uncovering what lies within: The first scientific account of cave-dwelling ground beetles (Coleoptera: Carabidae) in the Philippines with the description of a new genus, new subgenus, and four new species from Mindanao

For the first time in the Philippines, cave surveys were carried out in search of cave beetles. In this paper we describe a new troglobite genus, Kweba gen. nov., with two new species K. magbabaya sp. nov. and K. diwata sp. nov. We describe a new subgenus: Trogloabacetus subgen. nov. of the genus Metabacetus Bates, 1892, with the addition of two new species, M. (T.) baltazarae sp. nov. and M. (T.) desideratus sp. nov. from various limestone caves of Mindanao Island. Anaulacus (s.str.) fasciatus (Schmidt-Goebel, 1846) is also reported from the cave habitats. A key to the new and related genera, images of habitus and genitalia, and distribution maps are provided.

Cave beetle lineages gained genes before going down under: An example of repeated genomic exaptation?

The adaptation of animals to subterranean habitats like caves and aquifers stereotypically leads to dramatic trait-loss consequences like the lack of eyes and body pigmentation. These body plan regression trends are expected to be tied to gene loss as well. Indeed, previous studies documented the degeneration of vision genes in obligate cave dwellers. Contradicting this picture, the first broad-scale comparative transcriptome-wide study of gene content evolution in separate subterranean Australian and Mediterranean beetle clades unearthed evidence of global gene gain and retention. This suggests that the transition to cave life may be more contingent on gene repertoire expansion than contraction. Future studies, however, will need to examine how much the observed patterns of gene content evolution reflect subfunctionalization and fitness-securing genetic redundancy outcomes following gene duplication as opposed to adaptive trajectories.

Evidence of ancestral nocturnality, locomotor clock regression, and cave zone-adjusted sleep duration modes in a cave beetle

The small carrion beetle Ptomaphagus hirtus is an abundant inhabitant of the exceptionally biodiverse Mammoth Cave system. Previous studies revealed negative phototaxis and the expression of biological clock genes in this microphthalmic cave beetle. Here we present results from probing P. hirtus for the entrainment of locomotor rhythms using the TriKinetics activity monitor setup. Although curtailed by low adjustment frequency of animals to the test environment, the data obtained from successfully monitoring two animals in constant darkness (DD) and six animals exposed to 12 hour light-dark cycles (LD) revealed a strong effect of light on locomotor activity in P. hirtus. In LD, activity was prevalent during the artificial night phases while close to absent during the presumptive day phases, suggesting conserved nocturnality. Upon transitioning LD animals to constant darkness, none displayed detectable evidence of free-running activity rhythms, suggesting complete regression of the central circadian clock. Equally notable, overall locomotor activity of the two DD-monitored animals was about three-fold lower compared to LD animals due to longer rest durations in the former. We, therefore, propose the existence of cave zone-specific energy expenditure modes that are mediated through light schedule responsive modification of sleep duration in P. hirtus.

Consequences of the global climate crisis on the cave beetle Darlingtonea Kentuckensis Valentine based on thermal tolerance and dehydration resistance

Rising temperatures and diminishing groundwater availability due to the current climate crisis are predicted to expose cave faunas in eastern North America to unprecedented environmental conditions that could prove detrimental to their unique ecosystems. Organisms that inhabit relatively stable environments like caves are known to develop narrow physiological tolerances. Cave habitats with their organisms are simple ecosystems whose homogeneity offers an ideal system for testing the ability of a highly specialized fauna to tolerate abiotic changes. We tested the capability of a cave-specialized beetle in the eastern United States, Darlingtonea kentuckensis Valentine, to withstand future climatic shifts in its environment. We exposed individuals to a range of relative humidities and temperatures for 10 days. The data strongly suggest that there is a temperature threshold for the survival of D. kentuckensis, but it is a higher thermal tolerance than would be expected in an environment that has not fluctuated in recent evolutionary time and suggests remnant physiological characteristics of ancestral epigean carabids. Decreasing the relative humidity in the environment resulted in a much more dramatic decline in survival, indicating highly evolved specialization for constant high-humidity environments. The narrow humidity threshold in which troglobionts can survive may be a much more apparent limiting factor than temperature in adapting to climatic shifts within a cave environment.

Is the gut microbiome involved in adaptation of beetles to caves?

Cave beetles are endemic to one or few caves and live in a stable subterranean microclimate and permanent darkness. However, not much is known about the food sources of cave beetles and the share of autotrophic sources in their diet. Seven cave beetles were sampled seasonally from five Romanian caves together with a sampling of sediments and climatic measurements. Gut was extracted from the sampled specimens, and Illumina's 16S amplicon-based metagenomics sequencing protocol was applied to identify the gut microbiome. About 50% of the most abundant bacteria genera in the studied sediments are unknown taxa. The core elements of the sediments' microbiome were wb1-P19, Pseudomonas, and Lysobacter, all producers and decomposers of organic matter. Only Acinetobacter was shared for sediments and all cave beetles. The core bacteria in the gut of Leiodidae beetles of all five species were Vagococcus, Dysgonomonas, Candidatus Soleaferrea, and two unknown phylotypes. The cave Carabidae gut was dominated by Carnobacterium in one species and Enhydrobacter in the other, showing different food regimes within the Duvalius genus. Vagococcus was present in the gut microbiome of Leptodirini and Duvalius, a genus which might be involved in adaptation to life in caves, where food is scarce and autochthonous productivity is low. Higher body weight in cave beetles is another helpful strategy to cope with an infrequent food supply, as demonstrated by the presence of obesity-related gut microbiota representatives, Lactococcus and Serratia.

The ground beetles (Coleoptera, Carabidae) from the René Jeannel collection of the Babeș-Bolyai University Zoological Museum, Romania

This paper reviews the ground beetles from René Jeannel collection which is preserved in Zoological Museum of Babeș-Bolyai University. The illustrious coleopterologist, René Jeannel was a French entomologist, who worked between 1920-1930 as Deputy Director of the Institute of Speleology founded by Emil Racovitza, the first institute of its kind in the world. He was also a professor of general biology at the Faculty of Sciences of the University of Cluj Napoca. As well, in that period he published numerous articles on the systematics, phylogeny, biogeography and evolution of cave and endogenous beetles. In 1931, R. Jeannel left Romania to start working at the Muséum National d'histoire naturelle, whose director he was between 1945 -1951. During the 10 years of activity in Romania, he created and organized an important collection of ground beetles (Coleoptera, Carabidae). The total number of prepared and labeled specimens is 1672. The material was collected between 1921-1927, mostly in Transylvania, Romania. The collection includes 182 species from 56 genera and contains rare or endemic species. Among the endemic species we list: Pterostichus bielzii (Fuss, 1858), endemic to the Apuseni mountains, is present in the collection from 13 different locations; Nebria (Nebria) transsylvanica Germar, 1823, an endemic species in the Romanian Carpathians and in the southern part of the Carpathians in Ukraine; Platynus (Batenus) banaticus (I.Frivaldszky von Frivald, 1865) present in the collection from 3 locations. For the genus Carabus, representative species are Carabus (Megodontus) planicollis Küster, 1846, endemic species in Romania, and the Natura 2000 species Carabus variolosus Fabricius, 1787 and Carabus (Procerus) gigas (Creutzer, 1799). Among the Trechinae the most representative are the genus Duvalius, with four species: Duvalius cognatus subsp. longicollis Jeannel, 1928, D. laevigatus (Bokor, 1913), D. budae subsp. dioszeghyi Mallasz, 1928 and D. hegeduesii subsp. jonescoi (Jeannel, 1919), and the genus Trechus with 7 species, of which 3 are endemic in Romania: T. bannaticus Dejean, 1831, T. biharicus Meixner, 1912, and T. marginalis Schaum, 1862. The collection is a very valuable one, both from a historical and scientific point of view, because it offers an overview of the diversity and distribution of carabids in the karst areas of Romania, at the beginning of the 20th century.

Three new troglobitic Coarazuphium (Coleoptera, Carabidae, Zuphiini) species from a Brazilian hotspot of cave beetles: exploring how the environmental attributes of caves drive ground-beetle niches

Three new species of troglobitic beetles of the genusCoarazuphiumare described from specimens collected in iron ore caves in the Flona de Carajás in Brazil, doubling the number of known species for the Carajás region. The new species ofCoarazuphiumare morphologically similar to the already described species from the same region and are distributed in a small geographic range. From allCoarazuphiumspecies of the region, including the new ones, two stand out,C. spinifemurandC. xingusp. nov., which are the smallestCoarazuphiumspecies. Both species have shorter legs and antennae when compared to the others. The main characteristic that differentiatesC. xikrinsp. nov.andC. kayaposp. nov.from the other two species from the Carajás region,C. tapiaguassuandC. amazonicum, is that the new species have more numerous setigerous punctures dorsally on the head. With the three new species added to the six already described congeners, the area of intense mining of the Carajás region includes the highest diversity of obligatory cave-dwelling beetles in Brazil, representing a hotspot of cave beetles.Coarazuphium xikrinsp. nov.andC. amazonicumco-occur in some of the caves of the Carajás region, which is possible due to putative niche differentiation between the species. These findings highlight the importance of maintaining legal provisions that ensure the preservation of caves, especially those most relevant regarding physical and biotic aspects, which is crucial for the conservation of Brazilian subterranean biodiversity.

Rudogorites simonei gen. nov. and sp. nov. from Central Bosnia (Coleoptera: Leiodidae: Cholevinae: Leptodirini).

Dinaric karst in Western Balkans is especially biodiverse in cave beetle fauna. Despite the territory of Bosnia and Herzegovina being a relatively well-studied region, new species are still discovered and described regularly, even in recent times. Discoveries of new genera are, however, rare. Based on recently collected beetle specimens in the cave Lijina Peina near the town of Kreevo in the region of Bosansko Rudogorje in Central Bosnia, a new troglobiotic leptodirine genus Rudogorites gen. nov. and a single new species R. simonei sp. nov. are described. The region of Bosansko Rudogorje consists mainly of non-carbonate rocks, sandstones and polymetallic ore. In the area, there is a patch of isolated karst where a new endemic subterranean fauna has been found. An updated key to the Leptodirini genera of the Apholeuonus phyletic group is provided.

First insights into the origin of Iranian cave beetle diversity with description of two new species of the genus Duvalius (Carabidae)

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Smelling in the dark: Phylogenomic insights into the chemosensory system of a subterranean beetle.

The chemosensory system has experienced relevant changes in subterranean animals, facilitating the perception of specific chemical signals critical to survival in their particular environment. However, the genomic basis of chemoreception in cave-dwelling fauna has been largely unexplored. We generated de novo transcriptomes for antennae and body samples of the troglobitic beetle Speonomus longicornis (whose characters suggest an extreme adaptation to a deep subterranean environment) in order to investigate the evolutionary origin and diversification of the chemosensory gene repertoire across coleopterans through a phylogenomic approach. Our results suggested a diminished diversity of odourant and gustatory gene repertoires compared to polyphagous beetles that inhabit surface habitats. Moreover, S.longicornis showed a large diversity of odourant-binding proteins, suggesting an important role of these proteins in capturing airborne chemical cues. We identified a gene duplication of the ionotropic coreceptor IR25a, a highly conserved single-copy gene in protostomes involved in thermal and humidity sensing. In addition, no homologous genes to sugar receptors or the ionotropic receptor IR41a were detected. Our findings suggest that the chemosensory gene repertoire of this cave beetle may result from adaptation to the highly specific ecological niche it occupies, and that gene duplication and loss may have played an important role in the evolution of gene families involved in chemoreception. Altogether, our results shed light on the genomic basis of chemoreception in a cave-dwelling invertebrate and pave the road towards understanding the genomic underpinnings of adaptation to the subterranean lifestyle at a deeper level.

Living in isolation for almost 40 years: molecular divergence of the 28S rDNA and COI sequences between French and Polish populations of the cave beetle Speonomus normandi hydrophilus (Jeannel, 1907)

The paper gives the results of the first studies on the molecular divergence between native and non-native populations of Speonomus normandi hydrophilus (Jeannel, 1907). This species is endemic to Massif Arize in the Central Pyrenees (France), and represents highly specialised organisms that live underground. In 1982, one hundred specimens of S. normandi hydrophilus had been experimentally introduced into the Dzwonnica Cave (Poland). Since then, a numerous population has developed in the Towarna-Dzwonnica cave system, and the neighbouring Cabanowa Cave. After almost 40 years of isolation between native and non-native populations, the genetic variations were examined using the COI and 28S rDNA genes. Analyses of the haplotypes of 28S showed one common haplogroup, which confirms the origin of the Polish group. The differentiation of haplotypes for the COI marker was high for both the French and Polish populations. Altogether 18 haplotypes of this marker have been detected, 12 in the French population and 9 in the Polish. However, only a portion of the haplotypes is shared between the native and introduced population.

Complete mitochondrial genome of a cave dwelling Desmopachria (Insecta: Coleoptera: Dytiscidae) from the Eastern Amazon

Coleoptera presents most of the cave fauna biodiversity, with several troglobite species belonging to the aquatic family Dytiscidae. However, very little is known on both genetic and genomic diversity traits of Neotropical cave beetles. Thus, here we present the complete mitochondrial genome sequence of five specimens of Desmopachria collected in a ferruginous cave from Serra dos Carajás in Parauapebas (Pará, Brazil, Eastern Amazon). Besides the general characteristics of the mitogenome of the analyzed specimens, we present their phylogenetic position within the family, considering the available genome sequences of different subfamilies within Dytiscidae.

Geographically structured genetic diversity in the cave beetle Darlingtonea kentuckensis Valentine, 1952 (Coleoptera, Carabidae, Trechini, Trechina)

Cave beetles of the eastern USA are one of many poorly studied groups of insects and nearly all previous work delimiting species is based solely on morphology. This study assesses genetic diversity in the monotypic cave carabid beetle genus DarlingtoneaValentine 1952, to test the relationship between putative geographical barriers to subterranean dispersal and the boundaries of genetically distinct groups. Approximately 400bp of the mitochondrial cytochrome oxidase I (COI) gene was sequenced from up to four individuals from each of 27 populations, sampled from caves along the escarpments of the Mississippian and Cumberland plateaus in eastern Kentucky, USA. The 81 individuals sequenced yielded 28 unique haplotypes. Hierarchical analyses of molecular variance (AMOVA) within and among geographically defined groups tested two a priori hypotheses of structure based on major and minor river drainages, as well as genetic distance clusters defined a posteriori from an unrooted analysis. High genetic differentiation (FST) between populations was found across analyses. The influence of isolation by distance could potentially account for much but not all of the variation found among geographically defined groups at both levels. High variability among the three northernmost genetic clusters (FCT), low variability among populations within clusters (FSC), and low within-cluster Mantel correlations indicate the importance of unidentified likely intra-karst barriers to gene flow separating closely grouped cave populations. Overall phylogeographic patterns are consistent with previous evidence of population isolation among cave systems in the region, revealing geographically structured cryptic diversity in Darlingtonea over its distribution. The landscape features considered a priori in this study were not predictive of the genetic breaks among the three northern clusters, which are genetically distinct despite their close geographic proximity.

Mitochondrial sequence data indicate “Vicariance by Erosion” as a mechanism of species diversification in North American Ptomaphagus (Coleoptera, Leiodidae, Cholevinae) cave beetles

Small carrion beetles (Coleoptera: Leiodidae: Cholevinae) are members of cave communities around the world and important models for understanding the colonization of caves, adaptation to cave life, and the diversification of cave-adapted lineages. We developed a molecular phylogeny to examine the diversification of thehirtus-group of the small carrion beetle genusPtomaphagus. Thehirtus-group has no surface-dwelling members; it consists of 19 short-range endemic cave- and soil-dwelling species in the central and southeastern United States of America. Taxonomic, phylogenetic and biogeographic data were previously interpreted to suggest thehirtus-group diversified within the past 350,000 years through a series of cave colonization and speciation events related to Pleistocene climate fluctuations. However, our time-calibrated molecular phylogeny resulting from the analysis of 2,300 nucleotides from five genes across three mitochondrial regions (cox1,cytb,rrnL-trnL-nad1) for all members of the clade paints a different picture. We identify three stages of diversification in thehirtus-group: (1) ~10 million years ago (mya), the lineage that develops intoP.shapardi, a soil-dwelling species from the Ozarks, diverged from the lineage that gives rise to the 18 cave-obligate members of the group; (2) between 8.5 mya and 6 mya, seven geographically distinct lineages diverged across Kentucky, Tennessee, Alabama and Georgia; six of these lineages represent a single species today, whereas (3) the ‘South Cumberlands’ lineage in Tennessee and Alabama diversified into 12 species over the past ~6 my. While the events triggering diversification during the first two stages remain to be determined, the distributions, phylogenetic relationships and divergence times in the South Cumberlands lineage are consistent with populations being isolated by vicariant events as the southern Cumberland Plateau eroded and fragmented over millions of years.

The CAVEheAT project: climate change, thermal niche and conservation of subterranean biodiversity

One of the main challenges in disciplines such as ecology, biogeography, conservation and evolutionary biology is to understand and predict how species will respond to environmental changes, especially within a climate change context. We focus on the deep subterranean environment to minimize uncertainties in predictions, because it is one of the few ecosystems in nature whose environmental conditions are as homogeneous as those in the laboratory and their species cannot accommodate to changing conditions by behavioural plasticity, dispersal or microhabitat use (i.e., their only possibility to cope with climate change is to persist in situ). The hypotheses established for this project are based on the exciting results obtained in some of our previous studies, in which, we found that different subterranean beetle species living under different environmental conditions have identical/similar narrow thermal tolerance ranges, suggesting a lack of evolutionary adjustment to ambient temperature for these species. This could be due to the loss of some of the physiological mechanisms related to thermal tolerance, with a likely high metabolic cost, in a stable environment but with severe resource restrictions. However, the question that remains is to what extent this surprising narrow and homogeneous thermal niche is common for the whole subterranean biodiversity, and how this issue could determine the fate of subterranean biodiversity to climate change. In this project, we are testing for the generality of these exciting previous findings by studying the thermal niche (species acclimation abilities and thermal tolerances) of different lineages of cave beetles with different degrees of specialization to subterranean environments and from different geographical areas (Pyrenees and Cantabrian Mountains) (Suppl. material 1).

Limited thermal acclimation capacity in cave beetles

Thermal tolerance is a key vulnerability factor for species that cannot cope with changing conditions by behavioural adjustments or dispersal, such as subterranean species. Previous studies of thermal tolerance in cave beetles suggest that these species may have lost some of the thermoregulatory mechanisms common in temperate insects, and appear to have a very limited thermal acclimation ability. However, it might be expected that both thermal tolerance and acclimation ability should be related with the degree of specialization to deep subterranean environments, being more limited in highly specialized species. To test this hypothesis, we use an experimental approach to determine the acclimation capacity of cave beetles within the tribe Leptodirini (family Leiodidae) with different degrees of specialization to the deep subterranean environment. For this, we acclimate groups of individuals at a temperature close to their upper thermal limit (20ºC) or a control temperature (approximately that of the cave in which they were found) for 2 or 10 days (short- vs. long-term acclimation). a temperature close to their upper thermal limit (20ºC) or a control temperature (approximately that of the cave in which they were found) for 2 or 10 days (short- vs. long-term acclimation). Upper thermal limits (heat coma temperature, HC) are then measured for each individual using a ramping protocol (rate of increase of 1ºC/min) combined with infrared thermography and video recording. Preliminary results in a deep subterranean species (Speonomidius crotchi, with an intermediate degree of specialization) showed no significant effect of acclimation temperature in HC at any of the exposure times. Such reduced thermal plasticity could be also expected for other highly specialized subterranean species. The potential implications of these findings for subterranean biodiversity in a climate change context are discussed.

Radiation and ancestral range reconstruction of the cave beetle genus Anthroherpon (Coleoptera, Leiodidae, Leptodirini)

The genus Anthroherpon Reitter, 1889 is the most species-rich genus of the exclusively subterranean subtribe Anthroherponina. It comprises 26 species and 55 subspecies distributed in the Dinaric mountains which are known to be a world biodiversity hotspot for subterranean fauna. Most species are short-range endemics and more than half of the species are known only from a single cave, but the genus as a whole has a wide range. This study provides a comprehensive evolutionary analysis of the Anthroherpon radiation, using a dated molecular tree as a framework for understanding the diversification of the genus and reconstructing its ancestral range. We reconstructed the phylogeny of Anthroherpon using Bayesian analysis of six loci, both mitochondrial and nuclear, and we inferred the ancestral range of the genus using BioGeoBEARS. Our main findings show that Anthroherpon is monophyletic and started to diverge approximately in the Early Miocene (ca. 22 MYA). The genus has diversified entirely underground. Our results show that troglobitic lineages like Anthroherpon can disperse and diversify underground over a large geographic area during long periods of time. Biogeographic reconstruction of the ancestral range shows the origin of the genus in the area comprising three high mountains in western Montenegro: Dobreljica, Moračke planine, and Orjen. From this area the presumed ancestor dispersed to the other parts of its present range.

First record of a specialized hygropetricolous cave beetle, genus Croatodirus (Coleoptera: Leiodidae), in Slovenia

The cave hygropetric, an inaccessible subterranean habitat defined by films of water flowing down the cave walls, is renowned for its specialized filter feeding cave beetles. To date, no data on cave hygropetricolous beetles have been known for Slovenia, despite the existence of suitable karst areas. This paper reports on the first finding of a hygropetricolous cave beetle in Slovenia. A single female of a species belonging to the genus Croatodirus was discovered in the cave »Brezno treh src« on the Snežnik Plateau. The geomorphology and climate of the sampling site as well as the biology of hygropetricolous cave beetles are briefly described.

The cephalic morphology of free-living and cave-dwelling species of trechine ground beetles from China (Coleoptera, Carabidae)

Morphological adaptations of cave-dwelling organisms including different groups of Coleoptera have fascinated researchers since a long time. Nevertheless, very few detailed documentations of the anatomy of cave beetles using modern techniques are available. In this study, we describe and illustrate external and internal cephalic features of free-living and cave-dwelling trechine carabid beetles using digital microscopy, SEM, micro-CT, and computer-based 3D reconstruction. Morphological characteristics found in three selected species with different habitat preferences are compared. The following derived features distinguish a troglobite species (Sinaphaenops wangorum Ueno et Ran 1998) from a species living in the entrance of caves (Trechiotes perroti Jeannel 1954) and from a fully epigean species (Bembidion sp.): (1) the optic lobes are completely missing; (2) the head capsule, mouth parts, and antennae are distinctly elongated; (3) some muscle attachment areas are shifted; and (4) an additional dilator of the pharynx is present. Despite of conspicuous differences likely related with subterranean habits, the link of some cephalic features to this specific habitat preference remains uncertain.